Process for Preparing Saturated Branched Chain Fatty Acids

ABSTRACT

A process for preparing saturated branched chain fatty acids or alkyl esters thereof involving subjecting unsaturated fatty acids having 10 to 25 carbon atoms, alkyl esters thereof or mixtures thereof to a skeletal isomerization reaction in the presence of water or a lower alcohol at a temperature of about 240° C. to about 280° C. using a combination of a stericly hindered Lewis base and zeolite as a Brönsted or Lewis acid catalyst, and isolating saturated branched chain fatty acids or alkyl esters thereof or mixtures thereof from the reaction mixture obtained by the skeletal-isomerization reaction. The yield of said saturated branched chain fatty acids is ≧70 wt %. The stericly hindered Lewis base is a tertiary amine or phosphine with linear or branched C1 to C6 alkyl or phenyl groups attached thereto.

REFERENCE TO RELATED APPLICATION

This application claims the benefit of U.S. application Ser. No.12/767083, filed 26 Apr. 2010, which is incorporated herein by referencein its entirety.

BACKGROUND OF THE INVENTION

The present invention relates to a process for preparing saturatedbranched chain fatty acids or alkyl esters thereof involving subjectingunsaturated fatty acids having 10 to 25 carbon atoms, alkyl estersthereof or mixtures thereof to a skeletal isomerization reaction in thepresence of water or a lower alcohol at a temperature of about 240° C.to about 280° C. using a combination of a stericly hindered Lewis baseand zeolite as a Brönsted or Lewis acid catalyst, and isolatingsaturated branched chain fatty acids or alkyl esters thereof or mixturesthereof from the reaction mixture obtained by the skeletal isomerizationreaction. The yield of said saturated branched chain fatty acids is ≧70wt %. The stericly hindered Lewis base is a tertiary amine or phosphinewith linear or branched C1 to C6 alkyl or phenyl groups attachedthereto.

Environmental concerns over the use of petroleum-based materials in thelubricant industry have stimulated much research to find suitablealternatives. In this regard, lubricating fluids derived from renewablefats and oils are of interest because of their purported advantages overpetroleum-based materials (Hill, K., Pure Appl. Chem., 79: 1999-2011(2007)). Among the cited advantages of fatty acid derived lubricants aretheir lower toxicity, lower flammability since they have lower vaporpressures, and better biodegradability compared to petroleum-basedmaterials. Potential applications for such bio-based fluids can rangefrom lubricants, greases, additives, polymers, organic chemicals andmore. In fact, there are many commercial products in the market that arederived from renewable resources. For instance, polylactide polymers and1,3-propanediol, important intermediates for polymer syntheses, arederived from biomass sugars by fermentation and are cost competitivewith petroleum-based materials (Carole, T. M., et al., Applied Biochem.and Biotech., 113-116: 871-885 (2004)).

Vegetable oils also are promising candidates as replacemenst forpetroleum-based materials since they have excellent lubricity properties(Swern, D., Baily's industrial Oil and Fat Products, Third Edition, JohnWiley & Sons, New York). Although these oils themselves have somecommercial use, it is limited due to the presence of double bonds withintheir fatty acid alkyl chains which lead to oxidative stability problemswhen used at high temperature. Over the past decades, numerous chemicalmethods including electrophilic, nucleophilic, oxidative, andmetal-catalyzed reactions have been developed that convert the commonfatty acids found in natural fats and oils to novel oleochemicalcompounds that have improved and/or new properties over the startingfatty acids. For example, chemical processes for the modification of soyoil for use in greases, hydraulic and drilling fluids, and printing inkshave been developed (Erhan, S. Z. and M. O. Bagby, J. Am. Oil Chem.Soc., 68 (9): 635-638 (1991); Erhan, S. Z., et al., J. Am. Oil Chem.Soc., 69 (3): 251-256 (1992); U.S. Pat. No. 5,713,990).

Saturated branched-chain fatty acid isomers (sbc-FAs), commonly referredto as isostearic acids, are derived from unsaturated fats and oils as amixture of mono-methyl branched fatty acids (2, FIG. 1). Such mixturesof fatty acids are of commercial interest because they are liquid atlow-temperatures, have good lubricity properties, and have goodoxidative stabilities because of their lack of double bonds. Isostearicacid type products are currently used in the formulation of cosmetics,body washes, lubricants and fuel additives, surfactants, soaps, andcoatings. Approximately 100 million pounds of these acids are consumedglobally each year. Currently, the bulk of sbc-FAs 2 are obtained ascoproducts from reactions that predominantly produce dimer fatty acids(6, FIG. 1). The typical yields of sbc-FAs 2 are 25-50 wt %, and theirisolation and purification from the dimer acid 6 are labor-intensive.New processes that give higher yields and higher selectivity of sbc-FAsat a lower cost and with improved ease of isolation from othercoproducts would be highly advantageous;, such processes would expandtheir present use and/or open new outlets for these type of fatty acids.

We have developed a more efficient and economical process that maximizessbc-FAs production and minimizes the bimolecular reactions that producedimer products 6 as well as other unwanted coproducts (stearic 3,hydroxystearic 4, and γ-stearolactone 5; FIG. 1). We have also improvedcatalyst stability for multiple reuses.

SUMMARY OF THE INVENTION

In accordance with the present invention there is provided a process forpreparing saturated branched chain fatty acids or alkyl esters thereofinvolving subjecting unsaturated fatty acids having 10 to 25 carbonatoms, alkyl esters thereof or mixtures thereof to a skeletalisomerization reaction in the presence of water or a lower alcohol at atemperature of about 240° C. to about 280° C. using a combination of astericly hindered Lewis base and zeolite as a Brönsted or Lewis acidcatalyst, and isolating saturated branched chain fatty acids or alkylesters thereof or mixtures thereof from the reaction mixture obtained bythe skeletal isomerization reaction. The yield of said saturatedbranched chain fatty acids is ≧70 wt %. The stericly hindered Lewis baseis a tertiary amine or phosphine with linear or branched C1 to C6 alkylor phenyl groups attached thereto.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 shows products produced from zeolite-catalyzed isomerization ofoleic acid as described herein.

FIG. 2 shows GC spectra of the isomerized, hydrogenated and methylatedproduct Mixtures as described below: (A) with 2.5 wt % H-Ferr zeolite;(B) with 8 wt % H-Mordenite zeolite. Tridecanoate was the internalstandard. 2=methyl isostearate; 3=methyl stearate; 4=methylhydroxystearate; 5=γ-stearolactone; 6=C36-methyl ester dimer.

DETAILED DESCRIPTION OF THE INVENTION

The present invention concerns a process for preparing saturatedbranched-chain fatty acids or alkyl esters thereof. The process involvesthe steps of subjecting an unsaturated fatty acid or ester having 10 to25 carbon atoms, or mixtures of unsaturated fatty acids or esters to askeletal isomerization reaction in the presence of water or a loweralcohol at a temperature of about 240° to about 280° C. (e.g., 240°-280°C.) using a combination of a sterically hindered Lewis base and azeolite as a Brönsted or Lewis acid catalyst; the reaction time isgenerally about 4 to about 8 hours (e.g., 4-8 hours) and the amount ofLewis base utilized is generally about 2.5 wt % to about 20 wt % (e.g.,2.5 wt % to 20 wt %) to zeolite). The isomerized fatty acid mixture isthen subjected to hydrogenation to remove remaining double bonds withinthe fatty acid or ester chains to produce saturated branched-chain fattyacid or ester mixtures. The zeolite catalysts used in the process has alinear pore structure with a pore size that is small enough to retardoligimerization of unsaturated fatty acids or esters but sufficientlylarge enough to allow diffusion of the fatty acids or alkyl estersthereof into the zeolite structure where fatty acid or ester chainisomerization is catalyzed, The branched chain fatty acids or alkylesters or mixtures thereof are then isolated from the reaction mixtureand the isomerized fatty acid or ester or mixtures thereof hydrogenatedto remove residual unsaturation yield the desired saturatedbranched-chain fatty acid or ester mixture. The yield of the saturatedbranched-chain fatty acids is typically ≧70 wt %. The stericallyhindered Lewis base is, for example, a tertiary amine or phosphine withlinear or branched C1 to C6 alkyl or phenyl groups attached thereto.

When a starting material mixture contains both unsaturated fatty acidsor alkyl esters thereof, both branched chain fatty acids and alkylesters thereof can be produced because both can be isomerizedsimultaneously. The isomerization of unsaturated fatty acid case isincluded in the present invention.

The unsaturated fatty acid used as the starting material is generally afatty acid having unsaturated bonds and a total carbon number of 10 to25, preferably a total carbon number of 16 to 22. Considering industrialapplications, it is preferable that the major component of the startingmaterial has an average carbon number of 18. Unsaturated fatty acidshaving a total carbon number of this range are useful as startingmaterials for the synthesis of sbc-FAs for use in cosmetic bases, fibertreating agents, lubricating oil additives, etc.

With respect to the degree of unsaturation (i.e., the number ofunsaturated carbon-carbon bonds), any unsaturated fatty acid may be usedas long as one or more such bonds are present in the molecule.Specifically, the number of unsaturated bonds is generally 1 to 3,preferably 1. Octadecenoic acid is the most preferable. The presence ofan unsaturated bond in the molecule causes the formation of acarbocation as an intermediate, thereby facilitating the skeletalisomerization reaction. If a saturated fatty acid is used in largequantities as a starting material, formation of this intermediatecarbocation is hampered, thereby making it difficult for isomerizationto proceed.

Unsaturated fatty acids include oleic acid, palmitoleic acid, erucicacid, elaidic acid, linoleic acid, linolenic acid, and undecenoic acid,which can be derived from beef tallow, palm oil, safflower oil,sunflower oil, tall oil, rapeseed oil, soybean oil, or the like. Themixture that may be used as the starting material is a mixturecontaining two or more of these unsaturated fatty acids, or a mixturecontaining one or more of these unsaturated fatty acids and one or moresaturated fatty acids such as palmitic and stearic acids, various estersof the aforementioned unsaturated fatty acids, and the like. In the caseof a mixture, the content of the above-mentioned unsaturated fatty acidsis generally not less than about 40% by weight (e.g., not less than 40%by weight), preferably not less than 80% by weight (e.g., not less than80% by weight) in view of reaction rate and yield.

From the viewpoint of reaction selectivity, it is preferable that theabove-described starting material contains about 40 to about 100% byweight (e.g., 40 to 100% by weight) of octadecenoic acids, such as oleicacid and elaidic acid.

Alkyl esters of unsaturated fatty acids having a total carbon number of10 to 25 used as a starting material are those corresponding to theabove-described unsaturated fatty acids. That is, alkyl esters of theunsaturated fatty acids exemplified above are used. Although the alkylmoiety is not subject to limitation as to carbon number, its carbonnumber is normally 1 to 3, preferably 1. Specific examples of alkylesters include methyl esters, ethyl esters, propyl esters, and butylesters of the above-mentioned unsaturated fatty acids, with preferencegiven to methyl esters.

When a mixture is used as the starting material, a mixture that containsat least one alkyl ester of the above-described fatty acids is used.Specifically, it is a mixture of one or more alkyl esters of theseunsaturated fatty acids, or a mixture containing at least one alkylester of these unsaturated fatty acids and saturated fatty acids,various esters, etc. In the case of a mixture, the content of alkylesters of the above-mentioned unsaturated fatty acids is normally notless than about 40% by weight (e.g., not less than 40% by weight),preferably not less than 80% by weight (e.g., not less than 80% byweight) in view of reaction rate and yield.

From the viewpoint of reaction selectivity, it is preferable that theabove-described starting material be alkyl esters of unsaturated fattyacids containing about 40 to about 100% (e.g., 40 to 100% by weight) byweight of alkyl esters of octadecenoic acid, such as methyl oleate andmethyl elaidate, or a mixture thereof.

The present invention utilizes a combination of (1) zeolite as aBrönsted or Lewis acid catalyst and (2) a stericly hindered Lewis base.The Lewis base has a molecular size larger than the largest dimension ofthe open channels of the zeolite; the Lewis base interacts with theexternal active sites on the surface of the zeolite framework butbecause of their molecular size have limited access to the active siteswithin the zeolite channels. Such bases can neutralize the externalacidic sites on the surfaces of the zeolite framework but because oftheir size cannot access the interior acidic sites in the channels. TheLewis base may be an amine, phosphine, triarylphosphine,dialkylarylphosphine, trialkylphosphine, or mixtures thereof. Thephosphine may be methylphosphine, butylphosphine, dibutylphosphine,tributylphosphine, phenylphosphine, diphenylphosphine, or mixturesthereof. The triarylphosphine may be triphenylphosphine,diphenylphosphine, tri-p-tolylphosphine, tri(o-tolyl)phosphine,tri-m-tolylphosphine, trixylyl-phosphine, tris(p-ethylphenyl)phosphine,tris(p-methoxyphenyl)phosphine, tris(4-fluorophenyl)phosphine,tris(4-methoxyphenyl)phosphine, tris(dimethylamino)phosphine,tris(trimethylsilyl)phosphine, triisopropylphosphine, or mixturesthereof. The dialkylarylphosphine may be di-n-butylphenylphosphine,dicyclohexylphenylphosphine, or mixtures thereof. The trialkylphosphinemay be tri-n-butylphosphine, tricyclohexylphosphine,tri-n-octylphosphine, trimethyphosphine, triethylphosphine,triisopropylphosphine, tricyclopentylphosphine, or mixtures thereof. Theamine may be dimethylamine, trimethylamine, diethylamine, triethylamine,diisopropylamine, triisopropylamine, triphenylamine, diphenylamine, ormixtures thereof.

Zeolite used for the present invention has a linear pore structure ofpore size which is small enough to retard dimerization and large enoughto allow diffusion of branched chain fatty acids or alkyl estersthereof. Significant by-product formation due to dimerization isundesirable because it results in decreased yield of branched chainfatty acids, etc. However, insufficient diffusion of branched chainfatty acids, etc. is also undesirable because it results in decreasedapparent catalyst activity. To meet the above requirements, the meanpore size of zeolite is normally about about 4 to about 9 Angstroms(e.g., 4 to 9), preferably about 5 to about 8 Angstroms (e.g., 5 to 8),and more preferably about 6 to about 7 Angstroms (e.g., 6 to 7), varyingdepending on the total carbon number of branched chain fatty acids, etc.The term “linear pore structure” as used herein is a structure whereinpores are formed by at least linear continuous pathways.

In the present invention, any zeolite can be used, as long as it meetsthe above requirements. Generally, ferrierite type zeolite and mordenitetype zeolite are preferred from the viewpoint of pore size, heatresistance, acid resistance, and acid properties. The former isavailable only as a synthetic substance; the latter is available both asa natural substance and as a synthetic substance. The term “ferrieritetype zeolite as used herein, is a zeolite composed of two-dimensionalaluminum-silica network structure, with interconnecting channels betweenthe 8-membered-ring (MR) and 10-MR structures (Bekkem, H. V.,Introduction to Zeolite Science and Practice, 2nd Edition, Elsevier, NewYork, N.Y., 2001, pp. 1033-1053). The channels of commercially availableFerrierites typically contain an alkali metal (Na or K) or ammonium(NH₄) cation. For example, we examined K-containing Ferrierite with asilica/alumina (Si/Al) molar ratio of 17.5. The mordenite type zeolite,the highest in silicon content among naturally-occurring zeolites, is azeolite composed of oxygen 12-membered ring wherein the pores are formedmainly by tunnel-like pore pathways (Shokubai Koza, Vol. 10, edited bythe Catalysis Society of Japan, Kodansha Ltd. (1986)). Although thesezeolites can be synthesized by hydrothermal synthesis (J.C.S., 2158(1948)), they are also commercially available.

Although it is preferable from the viewpoint of catalyst activity thatthe cation in zeolite be a proton, a zeolite of the sodium type, or thelike, may be used in the reaction after being converted into the protontype by ion exchange. The Si/Al molar ratio of zeolite is preferablyabout 3 to about 300 (e.g., 3 to 300), more preferably about 5 to about100 (e.g., 2 to 100). The ratio is preferably not less than about 3(e.g., not less than 3) in view of catalytic activity, and not more thanabout 300 (e.g., not less than 300) in view of yield. The“silica/alumina ratio (molar)” can easily be determined by atomicabsorption photometry. Zeolite may be used in the reaction after apretreatment by ion-exchange, drying or burning.

In the present invention employing the above-described zeolite, thereaction is carried out in the presence of water or a lower alcohol.This is to suppress acid anhydride formation due to dehydration ordealcoholation of the starting material. This suppression isattributable to acid point modification of zeolite, such as conversionof Lewis acid point into Brönsted acid point. It is preferable to addwater when the starting material is unsaturated fatty acids; and analcohol when the starting material is esters of unsaturated fatty acids.The lower alcohol used is exemplified by alcohols having 1 to 4 carbonatoms. Specifically, methanol, ethanol, propanol, butanol etc. arepreferred, with a greater preference given to those having the samealkyl group as that of the starting fatty acid esters to be isomerized.

The isomerization reaction step in the present invention is carried outusing the above-described starting material, zeolite, etc. As forspecific reaction conditions, it is preferable that the reaction becarried out at about 240° to about 280° C. (e.g., 240° to 280° C.) inthe presence of about 0.1 to about 30 parts by weight (e.g., 0.1 to 30parts by weight) of zeolite and about 0.5 to about 5 parts by weight(e.g., 0.5 to 5 parts by weight) of water or a lower alcohol, based onabout 100 parts by weight (e.g., 100 parts by weight) of theabove-described unsaturated fatty acids and/or alkyl esters thereof.More preferably, the reaction is carried out at about 240° to about 280°C. (e.g., 240° to 280° C.) in the presence of about 1 to about 20 partsby weight (e.g., 1 to 20 parts by weight) of zeolite and about 1 toabout 3 parts by weight (e.g., 1 to 3 parts by weight) of water or alower alcohol, based on about 100 parts by weight (e.g., 100 parts byweight) of the above-described unsaturated fatty acids and/or alkylesters thereof.

Also, the reaction may be carried out in a closed system where thereaction pressure is generally about 2 to about 50 kgf/cm² (e.g., 2 to50 kgf/cm²). This is to prevent vaporization of water, alcohols andother low boiling substances in the system including those substancescontained in a catalyst.

Since the catalyst tends to be poisoned by coke, the reaction normallytakes about 1 to about 10 hours (e.g., 1 to 10 hours). If this problemis overcome, the reaction time can be shortened to several minutes oreven several seconds. Also, continuous reaction becomes possible.Excessively long reaction time tends to cause thermal decomposition,resulting in decreased yield.

The reaction apparatus used is preferably an autoclave, because apressurized reaction system is preferred. The atmosphere in theautoclave is preferably replaced with nitrogen or argon.

The product obtained by the above-described isomerization reactioncontains branched chain unsaturated fatty acids and/or esters thereof,when the starting material is an ester of an unsaturated fatty acids, ina high yield. The product further contains polymeric fatty acids, suchas dimer acids (polymeric fatty acid esters, when the starting materialis esters of unsaturated fatty acids). The branched chain fatty acids,etc. thus obtained normally have alkyl side chains of 1 to 4 carbonatoms. They are obtained as a mixture of many isomers with differentbranching positions.

Furthermore, in the present invention, branched chain saturated fattyacids (esters of branched chain saturated fatty acids, when the startingmaterial is esters of unsaturated fatty acids) can be obtained asfollows. Namely, removal of catalyst zeolite and polymeric materials byfiltration or distillation, the residue is hydrogenated in an autoclaveby a known method, such as the method using a hydrogenation catalyst(e.g., nickel or palladium/carbon), to yield a mixture of crude branchedchain saturated fatty acids (esters of branched chain fatty acids, whenthe starting material is esters of unsaturated fatty acids). Then thecrude product is purified by removing linear chain components by a knownmethod, such as the compression method, the Emerson method, and theHenkel method (U.S. Pat. No. 2,293,674; U.S. Pat. No. 2,421,157; U.S.Pat. No. 2,800,493; J. Am. Oil Chem. Soc., 45, 471 (1968)) orrecrystallization method, to yield branched chain saturated fatty acids(esters of branched chain saturated fatty acids, when the startingmaterial is esters of unsaturated fatty acids) of high purity.

The yield of the saturated branched chain fatty acids isgenerally >about 70 wt % (e.g., ≧70 wt %); preferably >about 71 wt %(e.g., ≧71 wt %); preferably >about 72 wt % (e.g., ≧72 wt %);preferably >about 73 wt % (e.g., ≧73 wt %); preferably >about 74 wt %(e.g., ≧74 wt %); preferably >about 75 wt % (e.g., ≧75 wt %);preferably >about 76 wt % (e.g., ≧76 wt %); preferably >about 77 wt %(e.g., ≧77 wt %); preferably >about 78 wt % (e.g., ≧78 wt %);preferably >about 79 wt % (e.g., ≧79 wt %). The yield of dimers (e.g., 6in FIG. 1) is generally ≦about 15 wt % (e.g., ≦15 wt %); preferably≦about 14 wt % (e.g., ≦14 wt %), ≦about 13 wt % (e.g., ≦13 wt %), ≦about12 wt % (e.g., ≦12 wt %), ≦about 11 wt % (e.g., ≦11 wt %), ≦about 10 wt% (e.g., ≦10 wt %), ≦about 9 wt % (e.g., ≦9 wt %), ≦about 8 wt % (e.g.,≦8 wt %), ≦about 7 wt % (e.g., ≦7 wt %), ≦about 6 wt % (e.g., ≦6 wt %),≦about 5 wt % (e.g., ≦59 wt %).

Unless defined otherwise, all technical and scientific terms used hereinhave the same meaning as commonly understood by one of ordinary skill inthe art to which the invention belongs. The term “about” is defined asplus or minus ten percent; for example, about 100° F. means 90° F. to110° F. Although any methods and materials similar or equivalent tothose described herein can be used in the practice or testing of thepresent invention, the preferred methods and materials are nowdescribed.

The following examples are intended only to further illustrate theinvention and are not intended to limit the scope of the invention asdefined by the claims.

EXAMPLES

The oleic acids 1 used in this study were a commercially availablematerial (Priolene™ 6936: 92.3 wt % oleic (C18:1), 3.1 wt % linoleic(C18:2), 0.4 wt % linolenic (C18:3), 4.2 wt % saturated fatty acids); agift from Croda International Co. (Gouda, The Netherlands)) and alaboratory grade oleic acid (91.2 wt. % C18:1, 6.1 wt. % C18:2, 2.7 wt.% saturated fatty acids), from Aldrich Chemical (Milwaukee, Wis.).Triphenylphosphine (TPP), hydrochloric acid (HCl), sulfuric acid(H2SO4), acetone, hexane, and methanol (MeOH) were from AldrichChemical. Mordenite (HSZ-640HOA, protonated (H⁺), 17.5-19.5 mol/molSiO₄/AlO₄) and Zeolite Ferrierite (HSZ-720KOA, potassium (K⁺). 17.5mol/mol SiO₄/AlO₄) were purchased from Tosoh Co. (Tokyo, Japan). Allother reagents used were of the highest purity available from commercialsuppliers.

Zeolite Catalyst Treatment: Solid K⁺-Ferrierite zeolite wasion-exchanged using the procedure described by Ngo et al. (Ngo, H. L.,et al., Eur. J. Lipid Sci. Technol., 108: 214-224 (2007)) but with someparts of the procedure modified. K⁺-Ferrierite zeolite (100 g) wastriturated with 300 mL of 1N HCl and 100 mL of deionized water at 55° C.for ˜20 h. The proton exchanged K⁺-zeolite was centrifuged (3000×g),washed by resuspention in deionized water (500 mL×5). The supernatanttested with pH paper. The pH of the supernatant solution was neutralafter the fifth wash. The solid was dried in an oven at 115° C. for 20h. Approximately 90 g of white solid was obtained. The ion-exchangetreatment converted the K⁺-zeolite into a H⁺-zeolite (the K⁺-zeolitesolid does not catalyze the isomerization reaction).

Synthesis and characterization of sbc-FA products: Sbc-FA products 2were obtained using conditions as previously reported (Ngo, H. L., etal., Eur. J. Lipid Sci. Technol., 108: 214-224 (2007)) but with someparts of the procedure modified. In general, a mixture of oleic acid 1(Priolene™, 50 g), H⁺-Ferr (2.5 g, 5 wt % of oleic acid), deionizedwater (1.8 mL), and TPP (7.5 wt % to H⁺-Ferr, 188 mg) was placed into a600 mL high pressure stainless-steel vessel (Parr Instrument, Moline,Ill.) equipped with a mechanical stirrer and an electric heating mantlewith temperature controller for isomerization reaction. The vessel wassealed and purged with 7.03 kgf/cm² N₂ (3× for 15 min). The reactor wasfilled with N₂ to ˜7.03 kgf/cm² and then heated to the desiredtemperature (240° C. to 280° C.) while mixing the contents. The pressureat the desired temperature was 14 to 28 kgf/cm². At the end of thereaction time (4-8 h), the reactor was cooled to room temperature, thepressure was released, and H⁺-Ferr solids were removed by vacuumfiltration using hexane and 0.45 μm HA membrane filter™ (MilliporeColo., Billerica, Mass.).

To characterize the isomerized crude unsaturated branched-chain (ubc)-FAproducts, 1 g of reaction liquid was hydrogenated using 5 wt % palladiumon carbon (Pressure Chemical Co., Pittsburgh, Pa.) as catalyst to give amixture of sbc-FA products. The product mixture was then methylated togive a mixture of sbc-fatty acid methyl esters (sbc-FAME) that werecharacterized by the following spectroscopies: Hewlett Packard (HP)Model 6890 gas chromatography instrument (GC, currently AgilentTechnologies, Santa Clara, Calif.), HP 5890 GC-mass spectrometry(GC-MS), matrix-assisted laser desorption/ionization-time of flight(MALDI-ToF) with a 4700 Proeomics Analyzer (Applied Biosystems,Framingham, Mass.), varian Gemini 200 MHz nuclear magnetic resonance(NMR) (Palo Alto, Calif.), and inductively coupled plasma atomicemission spectroscopy (ICP-AES). GC was used to determine the weightpercent compositions of the crude sbc-FA products (FIG. 1). GC-MS wasused to determine the molecular ions of the monomeric C18-components (2,3, 4 and 5). Mass spectra of the C36-methyl ester dimer 6 were acquiredby MALDI-ToF. NMR and ICP-AES were used to determine whether anyphosphorous compounds were leached into either the aqueous phase or oilproducts, respectively.

Zeolite Catalyst Regeneration: The used H⁺-Ferr catalyst (2.5 g)recovered from the isomerization process was transferred into a 150 mLcentrifuge flask with 1N HCl (5 mL) and deionized water (100 mL). Thesuspension was stirred at 55° C. for 24 h, cooled to room temperatureand centrifuged (3000×g). The aqueous phase was decanted into a vacuumfiltration device with a 0.45 μm HA membrane filter to capture theresidual fine solid particles in the aqueous phase that did not settleto the bottom of the flask during centrifugation. The solids in thecentrifuge flask were resuspended in deionized water (100 mL), mixedwell, and centrifuged. This step was repeated once more and thesupernatant tested with pH paper. The pH of the supernatant solution wasneutral after the second wash. The light brown H⁺-zeolites were dried at115° C. for 20 h before reuse.

Zeolite Catalyst Reuse Experiments: The recovered regenerated H⁺-Ferrsolid catalyst (2.5 g) was mixed with oleic acid (Priolene™, 50 g),deionized water (1.8 mL), and TPP (5 wt % to H⁺-Ferr (125 mg)) in a 600mL Parr reactor. The mixture was purged with N₂, sealed under N₂,stirred, and heated to 260° C. for 4 h. Isolation and characterizationof the product mixture were performed using the above procedures.

Analysis of Sbc-FAME: GC was used to determine the wt % composition ofproducts in the crude isomerized reaction mixtures after hydrogenationand methylation. GC was equipped with a capillary inlet injector (oncolumn mode) and flame ionization detector. The capillary column usedwas a HP Agilent DB5-HT column (30 m×0.1 mm×0.32 μm) attached to anAlltech Co., (State College, Pa.) deactivated fused silica guard column(2 m×0.32 μm). Helium was the carrier gas set at constant flow of 6mL/min. The detector temperature was set at 390° C. The oven temperatureprofile used was as follow: initial temperature 50° C., hold for 1 min.;ramp at 15° C./min. to 160° C.; ramp at 7° C./min. to 230° C.; ramp at30° C./min. to 380° C. hold for 10 min. The analytical method reportedpreviously (Ngo, H. L., et al., Eur. J. Lipid Sci. Technol., 108:214-224 (2007)) for characterizing crude sbc-FAME mixtures (FIG. 1)obtained from the zeolite-catalyzed isomerization of oleic acid was notsensitive enough to quantitate the dimer acid methyl ester coproduct 6in the crude product mixture. This is because 6 has higher molecularweight ([M]⁺=596 determined by MALDI-ToF) than the monomicC18-components (2, [M]⁺=298, 3, [M]⁺=298, 4, [M]⁺=314, and 5, [M]⁺=282determined by GC/MS). In this regard, the chromatographic peaks for 6were much broader than the peaks for the monomer products, which madequantitation of the former peaks difficult. To improve the resolutionand hence the quantitation of the chromatographic peaks of 6 theanalytical method was modified. The GC column helium flow was set at aconstant flow of 6 mL/min. This minor change enhanced thechromatographic resolution of the dimer ester coproducts and allowed fortheir quantitation.

Results and discussion: Table 1 (entries 1 & 2) list the resultsobtained for the analysis of the crude ester product reported previously(Ngo, H. L., et al., Eur. J. Lipid Sci. Technol., 108: 214-224 (2007))and when using the modified analytical method. With the new analyticalmethod, there was about 14 wt % dimer ester 6 in the crude productmixtures compared to the 5.5 wt % reported previously. The optimizedanalytical method detected the dimer coproducts at concentrations ≧2 wt% in the crude mixture which is important in that our improvedisomerization process only generates minor amounts of dimer estercoproducts (7.24% or less in Table 1).

One of our goals was to modify the zeolite catalyst in such a way so asto retain its activity while also enhancing its selectivity. Withoutbeing bound by theory, we hypothesized that formation of the dimer acids6 from oleic acid 1 arises via a bimolecular reaction that is catalyzedprimarily by the Brönsted acid sites located on the external surfaces ofthe H-Ferr particles, whereas formation of the monomer products sbc-FAs2, hydroxystearic acid 4, and γ-stearolactone 5 was postulated to becatalyzed by all Brönsted acid sites. The stearic acid 3 was also foundin the product mixture because of two reasons: 1) 2.7-4.2 wt % of 3 wasalready present in the starting fatty acids and 2) if the reactions gavelow conversions of oleic acid, thus hydrogenation of the oleic acidwould further enhance the amount of stearic acid 3. Without being boundby theory, we theorized that inactivating the active acidic sites on theexternal surfaces of H-Ferr particles with a Lewis base might suppressdimer acid 6 formation from oleic acid 1. With a judicious choice ofLewis base, for example one that was sufficiently bulky enough to beunable to penetrate deeply into the internal zeolite structure, wehypothesized that the acidic sites within the channels of the zeolitewould remain active. If this could be accomplished, then suchmodification would not significantly affect the activity of skeletalisomerization of oleic acid I that occurs within the interiors of thezeolite framework.

Initial results surprisingly showed that the addition of small amountsof a Lewis base such as TPP to the isomerization reaction significantlyreduced the formation of unwanted dimer acids. For example, in thepresence of 2.5 wt % of TPP (relative to zeolite catalyst) at 250° C.,the amount of dimer product 6 was surprisingly reduced from 13.6 wt % to6.33 wt % (Table 1, entries 2 & 4). However, a longer reaction time of22 hours (entry 4) versus 6 hours (entry 3) was needed to obtain asimilar degree of conversion of oleic acid 1 to products (Table 1,entries 2 and 4). We then increased the amount of TPP from 5 to 20 wt %(entries 5 & 6 respectively) to see whether the dimer acids could bereduced to less than 5 wt %. However, little difference in productdistribution was observed although a slight decrease in conversion wasnoted (Table 1, entry 6). It was subsequently found that increasing thereaction temperature from 250° C. to 280° C. surprisingly improved theconversion of oleic acid 1 to products (Table 1, entries 7-13). At 280°C., the TPP additive had a surprisingly significant affect on theisomerization reaction. As listed in Table 1 (entry 7), when thereaction was performed with 2.5 wt % H-Ferr without TPP, the wt%selectivity of the oleic acid to the products was 2, 66.5 wt %; 3, 4.46wt %; 4, 5.49 wt %; 5, 0.75 wt %; and 6, 22.8 wt %. With 2.5 wt % TPP(Table 1, entry 8) added to the isomerization process the conversion todimer acids surprisingly deceased to 7.24 wt % while the conversion tosbc-FAs 2 increased to 76.9 wt % with products 3, 4, and 5 amounting to5.98, 7.87, and 2.01 wt % respectively. Additions of 5 to 20 wt % TPP(Table 1, entries 9-13) also were examined to see if the dimer coproduct6 could be further reduced but minor difference in product distributionwas observed from those reactions run with 2.5 wt % TPP (Table 1, entry8). Table 1 (entries 10 & 11) show a set of two replicates, this wasdone to show the reproducibility of the reaction. Table 1 (entry 13)lists the reaction product distribution when performed on a 200 gramscale. The results were similar to those obtained at the 50 gram scalelevel (Table 1, entry 12).

We also found that this strategy worked with other types of zeolitecatalysts, highlighting the potential of external “deactivation” or“neutralization” of zeolite acidic surface (external) sites. For examplein a previous study by Tomifuji et al. (U.S. Pat. No. 5,677,473), it wasreported that an H-Mordenite zeolite could be used to isomerize oleicacid to sbc-FAs. We performed this reaction under conditions reported byTomifuji et al; however, the results obtained were significantlydifferent from that reported by Tomifuji et al. Without being bound bytheory, this could be due to the difference in catalyst, equipmentand/or methods of product analysis. Thus, it is better to compare theexperiments run with and without TPP (entries 1 to 4) since bothexperiments were performed using the same fatty acids, catalysts andequipment. Without TPP additive, at 280° C. for 6 h, 25.6 wt % yield ofdimer coproduct 6 was obtained (Table 2, entry 1) whereas with 5 wt % ofTPP added to the reaction the conversion to dimer coproduct 6 wassurprisingly 14.1 wt % (Table 2, entry 2). Increasing the TTP to 10 wt %surprisingly resulted in about 9.81 wt % of dimer 6 (Table 2, entry 3).The reaction also was performed at 250° C. for 6 h to examine whetherthe conversion of oleic acid 1 to dimer product 6 was influenced by thereaction temperature. The results obtained were not as good as thereaction performed at 280° C.; product yields were 2, 68.3 wt %; 3, 14.5wt %; 4, 3.6 wt %; 5, 5.82 wt % and 6, 7.78 wt%, with an oleic acidconversion of 91% (Table 2, entry 4). These results showed thatsterically hindered Lewis bases like TPP played an important role indeactivating or neutralizing the external Lewis/Brönsted acid sites ofthe zeolites.

The use of solid catalysts in these reactions facilitated the isolationand purification of the products which should improve the economics ofproducing sbc-FAs. It also is important to recycle the zeolite catalyststo help reduce the overall production costs. Several attempts were madeto regenerate the catalysts. The most efficient approach involvedwashing the used catalysts with solvents (e.g., polar solvent likeacetone or non-polar solvent like hexane) to remove adhered reactionproducts. The used zeolite catalyst was then transferred into acentrifuge flask containing dilute hydrochloric acid, heated at 55° C.for 24 h, recovered by centrifugation, washed with deionized water,dried in an oven to remove residual water at 115° C. for ˜20h, andreused to produce sbc-FA products. For the reuse experiments, thereactions were performed with 5 wt % H-Ferr at 260° C. for 4 h. Thishigher catalyst loading was needed because the reuse reactions were runat shorter reaction times. For the first use, 7.5 wt % TPP to H-Ferrcatalyst was added to the reaction mixture to ensure that sufficient TPPwas available to coat the external acid sites (Table 3, entry 1). Forthe second to the tenth reuse, 5.0 wt % TPP to H-Ferr was used becauseof concerns that repeated TPP loading could lead to catalystdeactivation problems (Table 3, entries 2-10). With this procedure, theused H-Ferr zeolite catalyst could surprisingly be recycled up to 10times without significant (i.e., between about 2 to about 5 wt % (e.g.,2-5 wt %) difference per cycle) loss of activity and selectivity (Table3). There was a slight decrease in activity after the 9^(th) reuse dueto minor catalyst loss during retreatment (Table 3, entries 9 & 10).Addition of TPP was needed for each cycle because, during regenerationof the catalyst with hydrochloric acid solution, the TPP formedphosphonium salts which were lost during the regeneration process. Theloss of phosphonium salts into the aqueous wash phase was confirmed byproton nuclear magnetic resonance. ICP-AES results showed that <0.01%phosphorous content was present in the sbc-FA products.

We have described the skeletal isomerization of normal chain unsaturatedfatty acids to sbc-FAs using Lewis base modified zeolite-catalysts. Theprocess can be used effectively to isomerize readily availablemonounsaturated fatty acids. This is important as currently mostlubricants are petroleum-based and their potential release into theenvironment can cause severe environmental burden owing to the poorbiodegradability of petroleum-based lubricants and hydraulic fluids.This process could benefit those interested in substituting the sbc-FAsfor the petroleum based materials.

Our results were superior to those previously reports because weobtained much higher molar conversions of oleic acid (>95%) andselectivities to sbc-FA products (about 70 to 80 wt %). The undesirabledimer coproduct was also obtained at much lower yield (about 5-10 wt %).The literature results typically only gave moderate conversions andselectivity. We have also shown that the catalysts were recyclable andreusable for at least ten times without significant loss of activity andselectivity.

All of the references cited herein, including U.S. Patents, areincorporated by reference in their entirety. Also incorporated byreference in their entirety are the following references: U.S. Pat. No.5,677,473; U.S. Pat. No. 5,713,990; U.S. Pat. No. 6,946,567; U.S. PatentApplication Publication 2003/0191330; EP 0774451A1 (1996); Bekkem, H.V., et al., Introduction to Zeolite Science and Practice, 2nd Edn.,Elsevier, New York, NY, 2001, pp. 1033-1053; Carole, T. M., et al.,Applied Biochemistry and Biotechnology. 113-116: 871-885 (2004); Erhan,S. Z., and M. O. Bagby, J. Am. Oil Chem. Soc., 68(9): 635-638 (1991);Erhan, S. Z., et al., J. Am. Oil Chem. Soc., 69(3): 251-256 (1992);Hill, K., Pure Appl. Chem., 79: 1999-2011 (2007); Ngo, H. L., et al.,Eur. J. Lipid Sci. Technol., 108: 214-224 (2007); Swern, D., Baily'sIndustrial Oil and Fat Products, Third Edition, John Wiley & Sons, NewYork; Tolman, C. A., Chem. Rev., 77: 313-348 (1977); Zhang, Z., et al.,J. Surf. Detergents, 7: 211-215 (2004).

Thus, in view of the above, the present invention concerns (in part) thefollowing:

A process for preparing saturated branched chain fatty acids or alkylesters thereof comprising (or consisting essentially of or consistingof) subjecting unsaturated fatty acids having 10 to 25 carbon atoms,alkyl esters thereof or mixtures thereof to a skeletal isomerizationreaction in the presence of water or a lower alcohol at a temperature ofabout 240° C. to about 280° C. using a combination of a stericlyhindered Lewis base and zeolite as a Brönsted or Lewis acid catalyst,and isolating saturated branched chain fatty acids or alkyl estersthereof or mixtures thereof from the reaction mixture obtained by theskeletal isomerization reaction; wherein the yield of said saturatedbranched chain fatty acids is ≧70 wt %; wherein said stericly hinderedLewis base is a tertiary amine or phosphine with linear or branched C1to C6 alkyl or phenyl groups attached thereto.

The above process wherein said process produces ≦about 10 wt % dimers.

The above process wherein said Lewis base is selected from the groupconsisting of amine, phosphine, triarylphosphine, dialkylarylphosphine,trialkylphosphine, and mixtures thereof. The process wherein saidphosphine is selected from the group consisting of methylphosphine,butylphosphine, dibutylphosphine, tributylphosphine, phenylphosphine,diphenylphosphine, and mixtures thereof. The process wherein saidtriarylphosphine is selected from the group consisting oftriphenylphosphine, diphenylphosphine, tri-p-tolylphosphine,tri(o-tolyl)phosphine, tri-m-tolylphosphine, trixylyl-phosphine,tris(p-ethylphenyl)phosphine, tris(p-methoxyphenyl)phosphine,tris(4-fluorophenyl)phosphine, tris(4-methoxyphenyl)phosphine,tris(dimethylamino)phosphine, tris(trimethylsilyl)phosphine,triisopropylphosphine, and mixtures thereof. The process wherein saiddialkylarylphosphine is selected from the group consisting ofdi-n-butylphenylphosphine, dicyclohexylphenylphosphine, and mixturesthereof. The process wherein said trialkylphosphine is selected from thegroup consisting of tri-n-butylphosphine, tricyclohexylphosphine,tri-n-octylphosphine, trimethyphosphine, triethylphosphine,triisopropylphosphine, tricyclopentylphosphine, and mixtures thereof Theprocess wherein said amine is selected from the group consisting ofdimethylamine, trimethylamine, diethylamine, triethylamine,diisopropylamine, triisopropylamine, triphenylamine, diphenyl amine, andmixtures thereof.

The above process further comprising (or consisting essentially of orconsisting of) a step wherein branched unsaturated fatty acids or alkylesters thereof obtained by the skeletal isomerization reaction arehydrogenated to yield branched saturated fatty acids or alkyl estersthereof.

The above process wherein said unsaturated fatty acids have 16 to 22carbon atoms.

The above process, wherein said process further comprises (or consistsessentially of or consists of) recycling said catalyst by washing saidcatalyst with a solvent and heating said catalyst in an acid solution,recovering said catalyst, washing said catalyst with deionized water,and drying said catalyst. The process, wherein said solvent is a polarsolvent or non-polar solvent. The process, wherein said catalyst isheated in an acid solution at about 55° C. (e.g., 55° C.) for about 24hours (e.g., 24 hours). The process, wherein said catalyst is dried atabout 115° C. (e.g., 115° C.) for about 20 hours (e.g., 20 hours). Theprocess, wherein the recycled catalyst has about 2 to about 5% (e.g., 2to 5%) loss of activity and selectivity.

Other embodiments of the invention will be apparent to those skilled inthe art from a consideration of this specification or practice of theinvention disclosed herein. It is intended that the specification andexamples be considered as exemplary only, with the true scope and spiritof the invention being indicated by the following claims.

1. A process for preparing saturated branched chain fatty acids or alkyl esters thereof comprising subjecting unsaturated fatty acids having 10 to 25 carbon atoms, alkyl esters thereof or mixtures thereof to a skeletal isomerization reaction in the presence of water or a lower alcohol at a temperature of about 240° C. to about 280° C. using a combination of a stericly hindered Lewis base and zeolite as a Brönsted or Lewis acid catalyst, and isolating saturated branched chain fatty acids or alkyl esters thereof or mixtures thereof from the reaction mixture obtained by the skeletal isomerization reaction; wherein the yield of said saturated branched chain fatty acids is ≧70 wt %; wherein said stericly hindered Lewis base is a tertiary amine or phosphine with linear or branched C1 to C8 alkyl or phenyl groups attached thereto.
 2. The process according to claim 1, wherein said process produces ≦about 10 wt % dimers.
 3. The process according to claim 1, wherein said Lewis base is selected from the group consisting of amine, phosphine, triarylphosphine, dialkylarylphosphine, trialkylphosphine, and mixtures thereof.
 4. The process according to claim 3, wherein said phosphine is selected from the group consisting of methylphosphine, butylphosphine, dibutylphosphine, tributylphosphine, phenylphosphine, diphenylphosphine, and mixtures thereof.
 5. The process according to claim 3, wherein said triarylphosphine is selected from the group consisting of triphenylphosphine, diphenylphosphine, tri-p-tolylphosphine, tri(o-tolyl)phosphine, tri-m-tolylphosphine, trixylyl-phosphine, tris(p-ethylphenyl)phosphine, tris(p-methoxyphenyl)phosphine, tris(4-fluorophenyl)phosphine, tris(4-methoxyphenyl)phosphine, tris(dimethylamino)phosphine, tris(trimethylsilyl)phosphine, triisopropylphosphine, and mixtures thereof.
 6. The process according to claim 3, wherein said dialkylarylphosphine is selected from the group consisting of di-n-butylphenylphosphine, dicyclohexylphenylphosphine, and mixtures thereof.
 7. The process according to claim 3, wherein said trialkylphosphine is selected from the group consisting of tri-n-butylphosphine, tricyclohexylphosphine, tri-n-octylphosphine, trimethyphosphine, triethylphosphine, triisopropylphosphine, tricyclopentylphosphine, and mixtures thereof.
 8. The process according to claim 3, wherein said amine is selected from the group consisting of dimethylamine, trimethylamine, diethylamine, triethylamine, diisopropylamine, triisopropylamine, triphenylamine, diphenylamine, and mixtures thereof.
 9. The process according to claim 1, further comprising a step wherein branched unsaturated fatty acids or alkyl esters thereof obtained by the skeletal isomerization reaction are hydrogenated to yield branched saturated fatty acids or alkyl esters thereof.
 10. The process according to claim 1, wherein said unsaturated fatty acids have 16 to 22 carbon atoms.
 11. The process according to claim 1, wherein said process further comprises recycling said catalyst by washing said catalyst with a solvent and heating said catalyst in an acid solution, recovering said catalyst, washing said catalyst with deionized water, and drying said catalyst.
 12. The process according to claim 11, wherein said solvent is a polar solvent or non-polar solvent.
 13. The process according to claim 11, wherein said catalyst is heated in an acid solution at about 55° C. for about 24 hours.
 14. The process according to claim 11, wherein said catalyst is dried at about 115° C. for about 20 hours.
 15. The process according to claim 11, wherein the recycled catalyst has about 2 to about 5 wt % loss of activity and selectivity. 